A delta-sigma modulator or sigma-delta modulator is a feedback system that employs simple circuit blocks to achieve high-resolution quantized output signals. The delta-sigma modulator is widely adapted to electronics circuits such as analog-to-digital converters (A/D), digital-to-analog converters (D/A) or frequency synthesizers, and is highly attractive in wireless communications due to its simplicity and low-power consumption. The radio-frequency (RF) bandpass delta-sigma modulator is one type of delta-sigma modulator that is well adaptable to RF signal reception and subsequent digitization without frequency down conversion.